Phương trình $\cos \left( {2x - \frac{\pi }{2}} \right) = 0$ có nghiệm là
A. ${\rm{x}} = \frac{\pi }{2} + \frac{{k\pi }}{2}.$
B. ${\rm{x}} = \pi + k\pi .$
C. ${\rm{x}} = k\pi $.
D. ${\rm{x}} = k2\pi $.
A. ${\rm{x}} = \frac{\pi }{2} + \frac{{k\pi }}{2}.$
B. ${\rm{x}} = \pi + k\pi .$
C. ${\rm{x}} = k\pi $.
D. ${\rm{x}} = k2\pi $.
Chọn A.
$\cos \left( {2x - \frac{\pi }{2}} \right) = 0 \Leftrightarrow 2x - \frac{\pi }{2} = \frac{\pi }{2} + k\pi \Leftrightarrow x = \frac{\pi }{2} + k\frac{\pi }{2},\left( {k \in \mathbb{Z}} \right).$
$\cos \left( {2x - \frac{\pi }{2}} \right) = 0 \Leftrightarrow 2x - \frac{\pi }{2} = \frac{\pi }{2} + k\pi \Leftrightarrow x = \frac{\pi }{2} + k\frac{\pi }{2},\left( {k \in \mathbb{Z}} \right).$